This invention relates to an electrophotographic printing process, and more particularly, it relates to a novel printing process based on electrophotography. 2. Description of the Prior Art
Fromthe viewpoint of facility in procedures, electrophotographic copying processes for many copies have been contrived, in addition to printing processes, as processes for the duplication of manuscripts in many copies. As a representative electrophotographic copying process for many copies, there is, for example, the electrostatic copying process, in which the image is exposed on a photosensitive layer that is photoconductive and has optical memory effects, and then the steps of charging, developing, transferring, and cleaning are repeated. This process is based on the principle that the exposed portion of the photosensitive layer turns electroconductive by its optical memory effects, thereby making it difficult to electrify that portion. As a photosensitive means using optical memory effects, known organic photosensitive means for an electrophotographic copying process can comprise poly-N-vinylcarbazole (PVK) and 2,4,7-trinitrofluorenone (TNF), wherein the organic photosensitive means contain, as the third ingredient, a leuco dye (E. Inoue, I. Shimizu, and Y. Nishino, Photogr. Sci. Eng., 22, 194 (1978), or a diazonium salt (J. Hanna and E., Inoue, ibid., 25, 209 (1981)).
In recent years, there was disclosed a photosensitive means for an electrophotographic copying process that comprises a photoconductive layer containing a hydrazone compound and a halogen-substituted anthracene derivative (Japanese Laid-Open Patent Application No. 60-164748).
Other processes include a copying process in which a switching element layer the electroconductivity of which varies in an electric field of high strength, is provided between a photosensitive layer and a photoconductive support. Here the image is recorded and stored in the switching element layer. For example, an electrophotographic system comprising a PVK-TNF photosensitive means and a Cu.TCNQ (7,7,8,8-tetracyanoquinodimethane) complex is known (Japanese Laid-Open Patent Applicatin No. 60-207143).
In the process comprising a photosensitive means based on the optical memory effects mentioned above, there are many problems with the known photosensitive means, such as the sensitivity of the photosensitive means being too low to give the desired optical memory effects, the capability of the photosensitive means to store the image being also too low, and the like.
On the other hand, in the second process comprising a switching element layer, the following problems occur. The photosensitive layer must be able to transfer both holes and electrons, so the materials available that can be used for the photosensitive layer are limited. The memory effects of a switching element layer depend greatly on the thickness of the layer, the dispersion ratio of the materials used for the layer, and the kind of binders contained in the layer, requiring the switching element layer to be prepared with great accuracy.
Also, as a problem common to the two processes mentioned above, a step of heating is needed to remove the image, thereby bringing about a complication in the structure of the apparatus for these processes.